The grenade machinegun is a powerful rapid-fire weapon which uses 25mm ammunition. The attached computer monitor appears to show the weapon's feed system and other details, although this is aesthetic and does not reflect actual use.
Outside of V.A.T.S., the weapon can be used for indirect fire over a considerable distance.
The grenade machinegun can fire a total of about 1995 standard rounds, the equivalent of 67 reloads, from full condition before breaking.
If the firing button is held as the weapon runs out of ammunition, the grenade machinegun will keep playing its firing animation, even though it is out of ammunition (no firing sound is played while this happens). The computer screen will also still keep scrolling as if firing.
Behind the scenes
The text on the screen of the gun is written in BASH script. The code itself wouldn't work as it contains syntax errors (No 'fi' ending the 'if' block.) When firing the text scrolls the same chunk of code.
pcps3xbox360Lonesome Road overrides some of the changes that have been made to the grenade machinegun in previous patches. With Lonesome Road installed and nothing else taking up space in your load order, the grenade's base damage is decreased to 0 and its item HP is reduced to 200.
pcxbox360ps3 Occasionally firing a multitude of rounds in quick succession will cause the sound to delay, hearing both the 'firing' and 'impact' sounds repeatedly trying to catch up, long after letting up on the trigger. If fired additional times when caught up in the delay, the hardware begins to lag as well, causing freezing and stuttering. This can often be fixed by firing one more time.
xbox360 The ammunition pack may become stuck to the back of the player character. To fix this, drop the grenade machinegun, equip another weapon. Drop the second weapon before picking up both weapons.
pcxbox360 The grenade machine gun doesn't inflict any damage on lakelurk kings at Blue Paradise Vacation Rentals. Lakelurk kings will die inside Camp Guardian caves. The coyote pup inside the truck trailer with at Canyon Wreckage will not die or take any damage, however the coyote den mother will. The coyote pack alpha on top of hill by the Canyon Wreckage can be killed with the grenade machinegun, but the other coyotes and pups will not take any damage with this weapon. The bark scorpion at the Ivanpah Dry Lake does not take any damage either. The Golden Gecko Hunter at the Crescent Canyon does not take any damage from the weapon but regular Golden Geckos do. Radscorpions just south of Black Rock Cave will not die or take any damage either from the grenade machinegun.
Grenade machinegun with the High-Speed Kit modification.